Wet process for the separation, isolation, and recovery of certain metallic and non-metallic constituents of waste slag from reverberatory refining of copper pyritic type ores



pt. 20. 1966 H. w. WILSON 3,273,997

WET PROCESS FOR THE SEPARATION, ISOLATION, AND RECOVERY OF CERTAINMETALLIC AND NON-METALLIC CONSTITUENTS OF WASTE SLAG FROM REVERBERATORYREFINING OF COPPER PYRITIC TYPE ORES Original Filed Dec. 26, 1963 4Sheets-Sheet 1 Fig. IA

AOIOIHNO NO], 019 MIXTURE} (FOR USE OF 50 SEE FIG, 24)

WA TE I? AQUEOUS AO/D SOLUTION 3-4.5 NORMAL, /00"-/35"E SLAG, DR);PULVER/ZED.

ST/I? TO DISSOLVE ADID- SOLUDLE PORTION OF SLAG.

F/L TER OR OENTR/FUSE INSOL UBLE I, ADD N/TRITE SALT SOLUTION f UNLESSAOID USED WAS NITRICIANDMIX,

2. ADD AQUEOUS AMMONIA SOLUTION WITH STIRR/NG TO 0/! 7.3'75

3. HEAT TO BOILING AND BO/L 2 MINUTES.

ACID/6 SOLUTION 0F SOLUBLE $405 or f5, 5/, 0a, Al, cu, Zn, Pb.

WASH TO REMOVE To ACID SOLUBLE SALTS i INSOLUDLE I (DISCARD) Hora/0 WWilson INVEN'I'OR.

P 20, 1966 H. w. WILSON 3,273,997

WET PROCESS FOR THE SEPARATION, ISOLATION, AND RECOVERY OF CERTAINMETALLIC AND NON-METALLIC CONSTITUENTS OF WASTE SLAG FROM REVERBERATORYREFINING OF COPPER PYRITIC TYPE ORES Original Filed Dec. 26, 1963 4Sheets-Sheet 5 SLA 670R), PUL VEfl/ZED) STIR TO DISSOLVE ACID- SOLUBLEPORTION OF SLAG F g 2A i V FILTER 0/? WAS/1' WITH CENTW/FUGE HOT WATER iTo H.6

SILICATE a SULFATE SALTS OF C0,Pb, Zn

I. .400 HOT WATERB STIR. 2. MAKE SLIGHTLY AMMONIACAL WITH NI! OH.

3, A00 AMMON/UM SALT- 4. DIGEST WITH HEAT8 STIR.

FIL TE I? 0/? FIL T E I7 0/? CE N TIP/F U65 INSOLUBLE I SOLUTION (0/5 CAR0) SOLUTION OF 60, Pb, 8 Zn I. OOIL OFF FREE NH 2. A00 A0 OH SOLUTION-3, HEA T UNTIL PREC/P/TZTE FORMS SOLUTION SOLUTION BO/L UNTIL FREE OF M1INSOLUBLE I- MIX W/TI-l MTER. FILTER 0R Ac/a/FY WITH H2504 GENTR/FUGE 3.HEAT TO SOIL/w. SOLUTION (DI CA D) L lit SOLUBLE F 5 DRYAT 212% ADDALCOHOL R F mam? SOLUTIONS sr/n SOLID LIQUID SOLUTION F/LTE'? sou/r10ELEC'WOLYTC CENTR/FUGE 1 (DISCARD) [AVENTOK RECOVERY or ZINC I. WASW/Th' WATER W F 2. mar 212%: I m

ca, so 2/50 INSOLUBLE was WITH ;/,0

Sept. 20, 1966 w. WILSON 3, 7

WET PROCESS FOR THE SEPARATIQN, ISOLATION, AND RECOVERY OF CERTAINMETALLIC AND NON-METALLIC CONSTITUENTS OF WASTE SLAG FROM REVERBEHATORYREFINING OF COPPER PYRITIC TYPE ORES Original Filed Dec. 26. 1963 4Sheets-Sheet 4 Ac/0/0 $0LUT/0N 0/ F 3/, 4/,800. g 2B 400 M1; 0H T0 0/-/22-25 OX/D/ZE A00 M51; 0H 7'0 0H 22 7.5 l, 4. HEAT T0 BOILING FILTER 0HGENTR/Fl/GE M'SOLUBLE SOLUTION 50L /0 L/OU/D [WASH WITH *4 I AC/OIFY mmH so 2 4 ELECTROLYTIC RE- F/L TE 0/? COVER) COPPER CENTR/FUGE SOLUTION IMIXED 15 378 A/ MISQLUBLE (H YDRA T E D OXIDE EITHER E/THEH V FILTER 0/?CONTROLLED DRY/1V6 cE/JTR/Fl/GE' (USE AS AOSORBE/VT} INSOLUELE on an /m0CALCl/VE Ms 8 my USE As P/GMENT ACTIVATE-a SILICA E/ HER CRYSTALL/ZE ADDH 0H Harold W Wf/SOfl 7 f L Fe 0/; T0 PHEc/P/TATE [M M 0R a 2 4 3 BY Q57)8 a Ammqys United States Patent 8 Claims. (Cl. 75-108) This is acontinuation of pending application for US. patent, Serial No. 333,333,filed December 26, 1963, now abandoned.

This invention relates to the recovery of certain metallic andnon-metallic constituents of waste slag produced as a result of smeltingcopper pyritic ores in a reverberatory copper refining furnace.

Due to the chemical composition of the ore and as a result of the way ithas been refined, the slag resulting as a waste product from thereverberatory refining of copper pyritic ore contains appreciableamounts of iron as metal and as iron oxides and silicates as well assome metallic copper, zinc, and lead, all in combination with alkalineearth metals in a matrix of metallic and non-metallic silicatescontaining residual amounts of metallic sulfides.

A principal object of this invention is the provision of a process forthe purpose of separating, isolating and recovering a major portion ofthe iron in said waste slag, and the recovery of the silica, calcium,copper, and zinc contained in the slag.

A more specific object of the invention is the treatment of such slagwith aqueous acid solutions and oxidants for the purpose of selectivelydissolving that portion of the slag consisting mainly of metallic iron,iron oxides, and metallic copper, lead and zinc and oxidizing them,especially the iron to ferric iron, while at the same time dissolvinglimited amounts of the silicate constituent of such slag. And, inparticular, it is a special object of this process to react such slagwith an acidic solution without causing a conversion of the silicadissolved by such acidic solutions into an insoluble silica gel(dehydrated) form until such time as it has been separated selectivelyfrom the other constituents found in the acid solubilized portion oftreated slag.

Still another object of the invention is to provide a process whereinthe acid-solubilized constituents of the slag are treated in such amanner that the iron (as trihydrated ferric oxide) and anyacid-dissolved silica (as dihydrated silicon dioxide) are firstseparated from the other acid-solublized components, and then the iron(as tri-hydrated ferric oxide) and the acid-dissolved silica (asdihydrated silicon dioxide) are separated from each other by conversionof the ferric oxide into an acid-soluble salt and by conversion of thedihydrated silicon dioxide into an acid-insoluble compound ofmonohydrated silicon dioxide.

These and other objects are accomplished by the process shownschematically in the several sheets of drawings in the nature of flowsheets accompanying this application, which illustrate variousalternatives in the process constituting this invention.

Briefly the process of this invention comprises:

(1) Treatment of the waste slag with aqueous solutions of approximatelyfour normal strength mineral acid or mixtures of mineral acidspossessing temperatures due to exothermic heats of dilution and ofsolution such that no ice external heat is required to effect maximumdissolution of the acid soluble metals and metallic oxides and metallicsilicates contained in the waste slag so as to be able to obtain, bymechanical separation, an insoluble residue and a solution containingsubstantially all of the acid soluble iron, silicon, aluminum, calcium,lead, copper, and zinc values in this slag;

(2) Oxidation of this solution by use of an aqueous solution of nitritesalts, which in acid medium liberate nitrogen dioxide and otheroxidizing nitrogen compounds which, in turn, oxidize the metallic ionsof the solution (especially the ferrous ions) without causing conversionof soluble silica into insoluble silica gel.

(3) Forming hydrated oxides of iron, silica, and aluminum which arereadily separated from the soluble compounds of calcium, lead, copperand zinc is accomplished by treatment of the acid soluble, oxidized,solution containing the soluble acids and acid soluble salts of iron,silica, aluminum, calcium, lead, copper and zinc with aqua ammoniasolution to a pH of 7.3-7.5 and heating to boiling in order to achievemaximum oxidation at optimum pH, and eliminate excess oxides of nitrogensuch as nitric oxide and nitrogen dioxide.

(4) Separating the hydrated oxides of iron and aluminum from thehydrated silica either by semi-drying and treating with sufiicient 36normal sulfuric acid to produce a 8-l0 normal sulfuric acid system, orby, drying at l00- 105 C. and treating with either 8-10 normal sulfuricacid or 12 normal hydrochloric acid to dehydrate the dihydrated silicaand convert it into monohydrated (insoluble) silica while formingsoluble salts of iron and aluminum chloride (or sulfate depending uponthe acid employed) which after dilution with 8-1O volumes of water andheating to boiling may be separated mechanically from the dehydratedsilica.

(5) Washing of the silica to free it of any occluded metallic salts andacids.

(6) Treating the silica-free acid solution of iron and aluminum acidsalts with aqua ammonia to reform the mixed iron aluminum trihydratedoxides, which after their mechanical separation from solution may bewashed, dried, and calcined to produce ferric oxide with a slightaluminum oxide contamination, or the solution may be treated withboiling alkali to form trihydrated ferric oxide and a soluble aluminatewhich may be separated from one another and the iron trihydrate may beconverted into ferric oxide by ignition, or the silica-free solution maybe concentrated by heating to effect crystallization of reasonably pure,aluminum salt-free ferric chloride or ferric sulfate.

(7) Recovering the lead by treatment of the solution containing solubleammonium salts of calcium, copper, zinc and lead, with sulfuric acid.

(8) Recovering the calcium by heating the resulting solution to boilingand While boiling adding sufficient aqua ammonia to adjust the pH to7.0-7.1. On continued boiling insoluble calcium sulfate hexahydrateforms which is separated from the solution and is then converted intocalcium sulfate dihydrate by drying at -105 C. temperature; and

(9) Recovering the copper and zinc (from the solution freed of lead andcalcium) by electrolysis for recovery of metallic copper and zinc, orremoval of these elements from solution may be accomplished by any ofseveral known hydrometallurgical processes.

In an earlier United States Patent 2,927,851, I have described thetreatment of waste slag derived from reverberatory refining of copperores with concentrated sulfuric and/or phosphoric acids to cause theformation of acid insoluble silica gel containing entrapped unreactedslag and acid, and acid salts derived from the acid used in treatment ofthe slag. As described in that patent 3 concentrated sulfuric and/ orphosphoric acids react with such slag to cause the formation of acidinsoluble silica gel, and I have found that certain concentrations ofhydrochloric and nitric acids will likewise cause the formation of acidinsoluble silica gel.

The invention hereinafter described is to treat such waste slag withcertain aqueous solutions of mineral acids and additional chemicalsubstances in such manner as to dissolve a maximum quantity of the slagtreated, while at the same time preventing any said insoluble gel fromforming, and hence is entirely different from the invention described inmy earlier patent. It has been found that the solution obtained as aresult of such treatment of the waste slag can be further treatedchemically to make possible selective separation, isolation, andrecovery of the following metals and compounds: acid salts of iron suchas ferric chloride and ferric sulfate, silicon dioxide (as such, or asadsorptive silica gel), ferric oxide, calcium sulfate, lead sulfate,copper and zinc metal.

In this description, wherever reference is made to slag such referenceis made to the waste product obtained from copper pyritic type oreswhich have been processed by the metallurgical process known asreverberatory refining. For use in the present process the slag isground until a minimum of 90% passes a 200 mesh U.S. Standard Sieve. Thefollowing approximate composition is typical of such waste slag:

28%32% iron expressed as Fe (and present as metal oxides, and silicate);

3238% silicon dioxide (present as mixed silicates of iron, calcium,aluminum, and magnesium);

8%10% expressed as CaO (present as basic silicate);

6%8% expressed as A1 (present as silicate);

2%3% zinc;

less than 0.5% lead;

0.3-0.5% copper; and

less than 1% sulfur (as metal sulfides).

In order to obtain the maximum degree of acid solvation of the slagexposed to treatment and in order to prevent the soluble dihydratedsilicon dioxide formed through acid hydrolysis of the acid solublesilicates of the slag from forming insoluble monohydrated silicondioxide (SiO 'H O) which during its formation creates a gel, it isnecessary to maintain an acid concentration of the aqueous aciddissolving medium in the range of 3.0 to 4.5 normal and a minimum watercontent in the slagacid-water system of not less than 65%. Use of acidsmore dilute than a 3.0 normal acid greatly reduces the solvationprocess, while acid solutions more concentrated than 4.5 normal causegel formation within minutes of combining the acid solution with theslag. At no time should the temperature of the slag-aqueous acid system(nor the acid solubilized portion after its removal from the insolubles)exceed 175 F., nor should either of the noted systems be allowed tostand for prolonged time periods.

The lower the acid concentration, the higher the water concentration, orthe lower the temperature, the longer the liquids can remain undisturbedwithout the occurrence of gelating. The liquid obtained with 4 normalhydrochloric acid containing 65% water and left standing undisturbed at80 F. temperature forms a gel in about 8 hours. The same-system gels tothe same degree of rigidity in approximately 2 hours merely by raisingits temperature to 178 F. The gel in both cases is irreversible andneither cooling nor dilution with water will effect re-solution of thegelled matter.

In accordance with the above, crushed waste slag is first treated withat least one acid selected from the group consisting of hydrochloric,nitric, nitrous, sulfuric, and mixtures of two or more of these acids.These acids may be used in conjunction with water soluble nitrite saltssuch as sodium nitrite or potassium nitrite. When nitric acid is used asthe slag dissolving acid, it it is impure with nitrogen dioxide contentthen the separate addition of nitrite salt is not required.Approximately 0.5% of the total acid concentration of the acids usedmust be nitric acid in order to insure that the copper remain dissolvedin the acid soluble solution during separation of the acid solublesolution from the acid insoluble residue. In the event that it is notdesired to recover all of the copper and its loss as sulfide may betolerated, nitric acid may be omitted from the acid initially used fordissolving the values to be recovered from the waste slag.

Use is made of the exothermic heats of dilution and solution incident tothe addition of the acid or acids to the Water in the preparation of theacid solution to be used as a solvent, by preparing the acid solutionimmediately prior to the addition of the acid solution to the dry slag.Use of the Warm acid solutions improves the solubilizing effectivenessas compared with the effectiveness of atmospheric temperature acidsolution solubilizing of atmospheric temperature slag. By preparing theacid solutions immediately prior to its addition to slag, both the costof providing external heat required to achieve maximum solvation of theacid soluble components of the slag and the inherent danger of at leastpartial gelation occurring as a result of localizing overheating of theslag-acid mixture from use of external heating are eliminated.

The available exothermic heats of dilution and solution when variousconcentrated acids are added to water initially at a temperature ofapproximately F. (atmospheric) in the preparation of 4 normal solutionsare indicated by the temperature rises resulting from the acid additionof the named acid to water to produce a 4 N solution of the acid.

Kind of cone. of acid Temperature of 4 N acid, F. used (at 80 F. temp.)

(From heat of dil. and soln.)

1101-12 N 102 HNO3-16 N 10s rr so as N 142 rrc1 12 N and rr so ss N HNO--l6 N and H2SO4-36 N 101 Temp. from reaction, F. Kind and temp. of acid(with heat of diln.):

HCl-4 at 102 F. 157 HNO 4 N at 108 F. 161 H SO 4 N at F. 173 H SO HCl-4N at 100 F. 136 H SO -HNO 4 N at 101 F. 138

Temp. from reaction, F. Kind and temp. of acid (cooled before use):

HCl4 N at 80 F. 132 HNO34 N at 80 F. 13s 11 50 1 N at 80 F 142 H SO-HCl--4 N at 78 F 116 H2SO4HNO34 N at 78 F. 11s

The percent slag dissolved by the use of various acid solutions variesbetween 40% and 55% with the higher percentage resulting from use ofhydrochloric and lower percentage resulting from use of mixed sulfuricand hydrochloric in a ratio of 1:1 by volumeor a normality ratio of 3:1.When the acid used for the initial treatment of the slag is sulfuric orsulfuric in combination with other acids most of the calcium dissolvedrecombines with the sulfate ion to form calcium sulfate hexahydratewhich for the greater part remains with the acid insoluble residue afterseparation from the acid soluble liquid portion. This calcium sulfatemay b recovered by leaching the residue with hot 5% ammonium chloridesolution in which the calcium salt is soluble. After separation thecalcium salt solution can be treated by various known methods forrecovery of calcium sulfate dihydrate or hemihydrate.

After the initial treatment of the slag, in which the acid solubleportion of the waste slag is dissolved, the acid insoluble residue isseparated from the acid soluble portion by vacuum filtration or pressurefiltration or by centrifuging. Any residual acid soluble material isremoved from the solid residue by washing the residue with water. Thewashings are combined with the acid soluble solution.

in this process, during or after dissolving the acid soluble portion ofthe slag, in order to effect separation and recovery of the iron, it isimperative that such iron be oxidized to its highest (ferric) valencestate since ferrous oxide hydrate cannot be removed effectively from theacid solution by presently known methods, while the ferric oxide hydratecan be completely removed by simple physical separation techniques. Theoxidation must be of such a nature that the soluble dihydrated silica ofthe solution is not converted into its insoluble gel form of monohydratebefore it has been separated from the acid insoluble components of theslag.

Oxidation of the iron of the system without dehydration of thedihydrated silica may be achieved in this process during the solvationaction of certain acid combinations or by treatment of the acidsolubilized fraction from use of other acid treatments after itsseparation from the acid insoluble residue. Examples of controlled acidsolvation and acid solvation in conjunction with controlled oxidationwhere the solubilized iron and silica along with other solubilizedconstituents of the slag are kept in solution for their selectiveseparation, isolation, and recovery are as follows:

Example 1 One hundred parts by weight (grams) of crushed slag arestirred into 300 parts by volume (ml.) of a freshly prepared 4 normalsolution of hydrochloric acid containing approximately one part byvolume of nitrogen dioxide containing nitric acid. The acid solution wasadded to the dry, pulverized slag in a suitable container all at onetime while thoroughly agitating the ingredients by mild stirring for atime period of 810 minutes. As the length of mixing time is shortenedbelow about 7 minutes the percentage of slag dissolved is diminished.The addition of the acid solution causes a reaction in which hydrogengas is liberated along with some hydrogen sulfide gas and is mildlyviolent in that the evolution of gas causes a great volume increasealong with rapid temperature rise, which reaches its maximum inapproximately 2 minutes. Mixing time in excess of 7-8 minutes does notappear to result in further solva-t-ion but appears to favor gelformation. Hence, separation of the liquid and solid phase from eachother as promptly as possible after sufficient mixing is importantparticularly when the acid concentration, water content of the system ortemperature are borderline, in which cases the composition could gelbefore the liquid and solid are separated. If all of the noted factorsare within specified limits, mixing time may be extended to at least onehour without gel formationbut since this does not appear to result inincreased solvation the additional mixing time is not warranted. In thisexample the temperature rise from heat of reaction reached 157 F. in 2minutes and the reacted mixture had a temperature of 147 F. at the endof 8 minutes.

One equation illustrating a possible reaction between the HCl and theiron ingredients of the slag-Fe, FeO, and Fe O in this example isExample 2 Another hundred parts by weight (grams) of the crushed slagwere mixed with 300 parts by volume (ml.) of a freshly prepared 4 normalsolution of nitric acid containing nitrogen dioxide as an impurity.Other than the use of the 4 normal nitric acid solution the process wasidentical to the one described in Example 1. The following equationsdescribe the reactions taking place between the iron ingredients of theslag and the nitric acid:

Example 3 Another one hundred parts by weight (grams) of crushed slagwere treated with 280 parts by volume (ml.) of a freshly prepared 4normal hydrochloric-nitric acid solution in the same manner as inExample 1 above where 4 normal hydrochloric acid was employed. In orderto insure conversion of intermediately formed ferric oxide and hydratedferric oxide into ferric chloride salts, the hydrochloric acidconcentration in the hydrochloric-nitric acid solution used exceeded thenitric acid concentration by at least 10%. When a 4 normal acid solutionprepared by combining 8 ml. of 16 N nitric acid, 12 ml. of 12 Nhydrochloric acid, and 38 ml. of water was used it provided insuficientavailable chloride ions to react with all ferric ions since a greatamount of the chloride ions are consumed from reaction with calcium ionsto form calcium chloride and the undissolved, insoluble portions offerric oxide and its hydrate remained with the acid insoluble residue,whereas a 4 normal solution prepared by mixing 8 ml. of 16 normal nitricacid, 16 ml. of 12 N hydrochloric acid, and 56 ml. of water convertedall of the ferric oxide and hydrate into ferric chloride.

Equations demonstrating these reactions are shown below:

+ 2FeC'l 51120 2N0 4H,

(3) 3FeCl +3HCl+HNO =3FeCl +NO+2H O Example 4 Another one hundred partsby weight (grams) of crushed slag were treated with 275 parts by volume(rnl.) of a freshly prepared H 30 solution of 4 normal concentrationwhich has been cooled before use to a temperature not in excess of 135F. there having been added approximately one ml. of nitric acidcontaining nitrogen dioxide to the H SO solution before its addition tothe dry slag. Equations showing the chemical reaction with this solventare:

Example 5 An additional grams of slag were treated with 300 ml. of afreshly prepared solution of 4 normal mixed acid in the proportion byvolume of one part of 36 N sulfuric acid to 4 parts of 12 N hydrochloricacid containing approximately 0.5% of nitrogen dioxide-containing nitricacid.

Example 6 An additional 100 grams of slag was treated with 300 ml. of afreshly prepared solution of 4 normal mixed acid 7' consisting of onepart of 36 N H 50 to 3 parts of 16 N HNO by volume.

In any of the foregoing examples, at the end of the 8-10 minute mixingperiod of the dry slag with the aqueous acid solution selected, the acidsolu-ble liquid portion is separated from the acid insoluble unreactedsolid portion by use of pressure or vacuum filtration or centrifuging orany other suitable physical separation process. The insoluble residue iswashed with water to free it of any occluded acid soluble liquid. Thewashings are added to the previously separated acid soluble liquidportion. The acid insoluble solid residue freed from any acid solublematerial by the water washing is discarded except when the solvationacid used was sulfuric. In this case the residue is treated further asnoted below for the recovery of calcium, zinc, and lead, if desired.

The acid soluble solution recovered by separation from the acidinsoluble residue, if it has not yet been oxidized at this stage, may betreated with any of the following oxidants to convert ferrous iron toferric iron: hydrogen peroxide, sodium or potassium peroxides,hypochlorous acid, sodium or potassium hypochlorite, sodium or potassiumchlorate, perchloric acid, and sodium and potassium perchlorates, or Nand N 0 derived from use of nitrite salts with acid. Examples of suchoxidation of ferrous iron when sulfuric acid was employed as the slagsolvation agent to produce ferrous sulfate are shown below:

Since, as indicated below, aqua ammonia is introduced into the acidicmedium after oxidation of ferrous iron to the ferric state in order tokeep copper and zinc ions in solution as soluble complexes, it ispreferable to employ oxidants such as hydrogen peroxide, hypochlorousacid, and perchloric acid which will leave acid residues in the systemrather than leaving the system alkaline with basic hydroxides. However,judicious use of alkaline oxidants such as sodium peroxide and acidicoxidants such as hydrogen peroxide in combination will result in a finalslightly acidic system requiring minimum amounts of aqua ammonia tocreate a pH of between pH 7.3 and 7.5 in which completed oxidation hastaken place to form the mixed hydrated oxides of iron, silica, andaluminum as insolubles and the copper and zinc in soluble form to allowseparation, of the one group from the other.

If the separated acid soluble fraction was not treated with any of theabove named oxidants and except when nitric acid containing nitrogendioxide was used in the slag dissolving process, the separated acidsoluble portion is treated with a water solution of a water solublenitrite salt such as sodium or potassium nitrite or the like.

Since in using acids other than nitric acid containing nitrogen dioxideas the solvation acids the dissolved iron in the acid soluble portionexists as ferrous iron predominantly. In order to achieve optimumseparation of the iron from the acid soluble fraction it is necessary toconvert the iron from the ferrous state to the ferric state. Thisconversion is accomplished through the reaction of the nitrite saltintroduced with the acid to cause oxidation of the iron without causingdehydration of the soluble dihydrate or silica. Equations illustratingthese reactions are shown below:

It will be noted that in all of the examples of this process thatoxidation of the iron is brought about by the combined effect of thenitrate and/or nitrite radicals in the presence of free hydrogen ions ofthe acid present whether it be nitric acid, hydrochloric acid, sulfuricacid, or mixtures of such acids where nitrogen dioxide as such activitybrings about the actual oxidation of the system.

The nitrite salt solution may be added either during the acid solvationtreatment or to the acid soluble solution after its separation from theinsoluble residue. For each parts by weight of slag approximately 8parts by weight of the nitrite salt is required. Use of smaller amountsof nitrite salt results in incomplete oxidation, while more than thisamount produces no additional benefits. The equations above indicatethat definite amounts of free acid favor maximum formation of maximumamounts of the desired nitrogen dioxide for optimum oxidationconditions. A three to five minute period of contact of the nitrate saltwith the acid medinum is sufficient to achieve complete oxidation of alliron in the system.

The acidic acid soluble, oxidized fraction now having its iron contentall in the ferric state is neutralized by adding an aqueous ammoniasolution (15 normal) until the pH of the solution is between pH 7.2 andpH 7.5. Weaker solutions of the aqueous ammonia may be used with nodifferent effect other than increasing the volume of the system. Use ofaqua ammonia to produce pH values above 7.5 contribute no value, whileat the same time such use would cause use of unnecessary amounts ofadditional chemicals in later phases of the process. pH values between7.0 and 7.2 or lower (into the acid range) are totally unsatisfactory inthat there would be insuflicient ammonium ion for formation of thetrihydrated ferric oxide and formation of the ammonium complexes ofcopper and zinc. The use of alkali hydroxides instead of aqua ammonia toaccomplish the pH change results in the hydrated ferric oxide beingcontaminated with insoluble copper and zinc compounds. The aqua ammoniaaccomplishes conversion of the iron and aluminum present in solutioninto their respective trihydrated oxides and conversion of thedihydrated silica into silica monohydrate. These coprecipitated oxidesof iron, aluminum, and silica are easily separated from the liquid byvacuum filtration or pressure filtration or by centrifuging and can bewashed free of the major portion of any occluded calcium, lead, copper,and Zinc soluble salts by use of very dilute aqua ammonia water (0.1% NHsolution) without loss through iron sol formation. The solution afteraddition of aqua ammonia solution to the specified pH is heated toboiling to insure total oxidation of the iron (which is optimum at pH ofapproximately 7.0) and boiling the solution for one to two minutesassures conversion of any colloidal sol of the hydrated iron oxide to agel, while at the same time eliminating all unused nitrogen dioxide(note Equations 2, 3 and 4 following).

The following equations illustrate the mechanism of formation of thetrihydrates of iron and aluminum and the elimination of the unusednitrogen dioxide from the system:

Due to the physical nature of the coprecipitate of ironaluminurn-silicahydrated oxides it can be dissolved in acid and reprecipitated as oftenas desired provided it is not allowed to lose its water of hydration.Selective drying at varied temperatures produced adsorbents havingcapacities of adsorption of liquids and gases. Drying and calcinationresults in products capable of being used as combination color andextender, surface coating pigments. If it is desired, after removal ofthe major portion of free water (80%90%) by drying, the coprecipitatecan be treated with either 12 normal hydrochloric or 36 normal sulfuricacid which will dissolve the iron and aluminum while dehydrating thehydrated silica into a dehydrated silicon dioxide. After water dilutionof the acid treated semidried or dried coprecipitate with 8 to 10volumes of water the resulting mixture can be filtered or centrifuged toseparate the dehydrated silica from the soluble iron and aluminum acidsalts. Washing of the separated silica with hot water frees it of anysoluble contaminants and produces a product which can be dried and usedas such or which maybe processed by known methods to activate for use asan adsorbent material. Treatment of the acid solution of iron andaluminum with aqua ammonia :solution to a pH of 3.2 will causeprecipitation of the iron as trihydrated oxide. The precipitate (by useof aqua ammonia) of the iron hydrated oxide may be dried and calcined toa product consisting predominantly of ferric oxide and may be used assuch. If it is desired, instead of converting the iron into thetrihydrated oxide form by neutralizating to pH 3.2 with aqua ammonia toeffect precipitation of the hydrated oxide, the solution of acid saltsmay be processed by selective crystallization to produce ferric chlorideor ferric sulfate depending upon the acid solution used in dissolutionof the ferric-aluminum hydrates from the silica.

The ammoniacal solution resulting from removal of the hydrates of iron,aluminum, and silica and containing soluble salts of lead, calcium,copper, and zinc (unless sulfuric acid was employed as the initial acidsolvation agent which would have caused formation of lead sulfate andcalcium sulfate insoluble in the medium and thus not present in thesolution) is heated to boiling and acidified with sufficient sulfuricacid to cause formation of lead sulfate and calcium sulfate. The leadsulfate formed is insoluble in the sulfuric acid and may be removed as aSolid by filtration or centrifuging. The lead-free acidic solution isneutralized to pH 7.0 to 7.1 with aqua ammonia and heated to boiling tocause the formation of insoluble calcium sulfate hexahydrate which isremoved by filtration or centrifuging. The calcium salt is dried at 100105 F. temperature after which it is washed with alcohol to removeoccluded ammonium salts and then washed with water, yielding relativelypure calcium sulfate dihydrate. Removal of the lead and calcium leaves aslightly ammoniacal solution containing soluble compounds of copper andzinc. Recovery of these elements in metallic form can be accomplished byknown methods of electrolytic deposition. Their isolation and recoverymay also be accomplished by conversion into sulfide form, followed byacid dissolution and metallic displacement methods.

When sulfuric acid is employed as the solvation agent, calcium, zinc,and lead will be found with the acid insoluble residue as sulfates.After washing this residue to free it of all acid and acid solubles, itis mixed with a few volumes of hot water, made slightly alkaline withgas ammonia (to insure no solvation of silica), and treated withsufiicient ammonium salt of sulfate, chloride, or nitrate to effectsolvation of the calcium, zinc and lead sulfates. The mixture isdigested while heating to cause the soluble complexes of calcium, zinc,and lead ammonium sulfates to form. Separation of the soluble complexesby filtration or centrifuging followed by washing the insoluble residuewith water containing 2%3% ammonium salt results in a solution which istreated as follows for recovery of its calcium, zinc, and leadcompounds. The solution is heated to boiling and boiled to the absenceof free ammonia (no odor) after which 10 sufficient aqueous alkali (NaOHor KOH) solution is added to cause the formation of insoluble zinc andlead hydroxides as shown below:

Excess alkali or prolonged boiling are to be avoided to minimize theconversion of zinc and lead hydroxides into their soluble forms ofzincate and plumbate as shown below:

The insoluble zinc and lead hydroxides are separated from the solutionby filtration or centrifuging and after washing are mixed with a fewvolumes of water and mildly acidified with sulfuric acid, which onboiling causes the formation of insoluble lead sulfate and a solution ofzinc sulfate. The lead sulfate is separated by filtration orcentrifuging from the zinc sulfate solution which is then madeammoniacal wit-h aqua ammonia to permit electrolytic recovery ofmetallic zinc.

The solution remaining after separation. of the zinc and lead hydroxidesis boiled until free of ammonia as noted by no liberation of ammoniawhen treated with small additional amounts of alkali hydroxide. Duringthe boiling of the solution to an absence of ammonia, hydrated calciumsulfate is formed, which may be removed by filtration or centrifuging.Complete precipitation and total conversion of all calcium in the systemmay be obtained by cooling the solution freed of ammonia and dilutingthe solution with alcohol. A small loss of calcium is encountered ifalcohol is not introduced. The separated hydrated calcium sulfate isdried at 105 C. temperature, and after drying is washed withwateralcohol mixture first and then by water to remove soluble occludedsodium salts present. The calcium sulfate dihydrate is then dried foruse.

The separated mixture of lead hydroxide and zinc hydroxide is washedfree of any occluded material with water and then added to two or threevolumes of water. Sufficient sulfuric acid is added to dissolve thehydroxides and the solution heated to boiling during which time leadsulfate (insoluble) is formed in a solution of zinc sulfate. The leadsulfate is separated by filtration or centrifuging and after washingwith water'free Otf any zinc and dried is ready for use. The solution ofzinc sulfate is treated with aqua ammonia to slight excess and theammoniacal solution electrolyzed for recovery of metallic zinc.

The acidic solution of iron, silica, aluminum, and copper containingonly trace amounts of calcium and zinc recovered from the solvation ofthe slag with sulfuric acid is treated with aqua ammonia solution (15normal preferably) until the solutions pH is slightly over 7 after whichsufiicient oxidant from the group comprised of peroxides, chlorites,chlorates, or perchlorates is added to convert all ferrous iron intoferric iron. If acid residue oxidants such as hydogen peroxide are usedfor oxidation the addition of additional aqua ammonia is made tomaintain a pH of the solution between pH 2.5-6.5, which range is optimumfor quick, complete conversion of ferrous iron to ferric iron. When thesolid matter formed in the solution retains a bright, red-orange colorupon addition of additional aqua ammonia, complete oxidation has beenaccomplished. If the solution and precipitate turn black, blue, or darkgreen at the point of addition of the added aqua ammonia this isevidence of incomplete oxidation showing the need for addition ofadditional oxidant. After oxidation is completed additional aqua ammoniais added until the pH is between pH 7.3 to 7.5 after which the liquid isheated to boiling and boiled approximately 2 minutes to effectcoagulation of the hydrated oxides which is noted by the color of thesolid mater in the solution changing from red-orange to Indian redordeep reddish-brown in color. Separation of the hydrated oxides from thesolution and the treatment for recovery of copper from the solution andseparation, isolation, and recovery of ferric iron acid salts or oxide,the monohydrated silica, or combinations of mixed dehydrated oxides ofiron, silica, and aluminum is performed in the same manner as has beendescribed when acids other than sulfuric were used in the initialsolvation of the slag.

What is claimed as new is 'as follows:

1. A Wet process for the separation, isolation and recovery of the acidsoluble metallic and non-metallic values in waste slag resulting fromthe reverbratory refining of copper pyritic type ores which comprises:

crushing the slag;

adding a warm solution of at least one mineral acid to said crushedslag, said solution having a normality of 4 at the time it is added tothe slag;

mixing the slag and acid for not less than 8 minutes under conditionssuch that the two are not permitted to reach a temperature of 175 F.,whereby the formation of silica gel is avoided;

separating the resulting solution from the solid insoluble residue; and

recovering the soluble iron, lead, copper, calcium, silicon, zinc andaluminum values originally present in said slag from said solution.

2. The process of claim 1 wherein the mineral acid is selected from thegroup consisting of hydrochloric, nitric, and sulfuric and mixtures ofsaid acids with one another and with nitrous acid.

3. The process of claim 1 wherein the recovery of the values in saidsolution after the solution resulting from treatment of the crushed slagwith said mineral acid has been separated from the insoluble residue,includes: addition of a sufiicient amount of a nitrite salt to thesolution to oxidize all of the iron present in the solution to ferriciron; addition of a sufiicient amount of ammonia to raise the pH tobetween 7.2 and 7.5 and boiling the solutions to precipitate hydratedoxides of iron, silicon and aluminum.

4. The process of claim 1 wherein mineral acid is a mixture ofhydrochloric and nitric acids.

5. A wet process for the separation, isolation and recovery of the acidsoluble metallic and non-metallic values in waste slag resulting fromthe reverberatory refining of copper pyritic type ores which comprises:

crushing the slag;

preparing a 4 normal solution of at least one mineral 'acid selectedfrom the group consisting of HCl, HNO H 50 by dilution of a strongersolution of said acid; adding the warm solution of said mineral acid tosaid crushed slag, said solution having a normality of 4 at the time itis added to the slag and retaining at least a substantial portion of theheat of dilution and solution incident to the preparation of said acid;

mixing the slag and warm acid for not less than 8 minutes underconditions such that the two are not permittedto reach a temperature of175 F whereby the formation of silica gel is avoided;

separating the resulting solution from the solid insoluble residue; and

recovering the soluble iron, lead, copper, calcium, silicon, zinc andaluminum values originally present in said slag from said solution.

6. A wet process for the separation, isolation and recovery of the acidsoluble metallic and non-metallic values in waste slag resulting fromthe reverberatory refining of copper pyritic type ores which comprises:

crushing the slag;

adding a warm solution of sulfuric acid to said crushed slag, saidsolution having a normality of 4 at the time it is added to the slag;

mixing the slag and acid for not less than 8 minutes under conditionssuch that the two are not permitted to reach a temperature of F.,whereby the formation of silica gel is avoided;

separating the resulting solution from the solid insoluble residue; and

recovering the soluble iron, copper, silicon, and aluminum valuesoriginally present in said slag from said solution and the lead, calciumand Zinc values in said slag from said insoluble residue.

7. A wet process for the separation, isolation and recovery of the acidsoluble metallic and non-metallic values in waste slag resulting fromthe reverberatory refining of copper pyritic type ores which comprises:

crushing the slag;

adding a warm solution of at least one mineral acid to said crushedslag, said solution having a normality of 4 at the time it is added tothe slag;

mixing the slag and acid for not less than 8 minutes under conditionssuch that the two are not permitted to reach a temperature of 175 F.,whereby the formation of silica gel is avoided;

separating the resulting solution from the solid insoluble residue;

adding a nitrite salt to the separated solution to oxidize all of theiron therein to ferric iron; adding ammonia to the resulting solution toproduce a pH between 7.2 and 7.5;

boiling the solution thereby precipitating the iron, silicon andaluminum therein as a mixture of hydrated oxides;

separating the precipitate from the solution;

acidifying the precipitate to dissolve the iron and aluminum therein;

removing some of the water present by heating the acidified solution;

and separating the resulting silica gel from the remaining liquid. 8. Awet process for the separation, isolation and recovery of the acidsoluble metallic and non-metallic values in waste slag resulting fromthe reverberatory refining of copper pyritic type ores which comprises:

crushing the slag; adding a warm solution of at least one mineral acidto said crushed slag, said solution having a normality of 4- at the timeit is added to the slag;

mixing the slag and acid for not less than 8 minutes under conditionssuch that the two are not permitted to reach a temperature of 175 F.,whereby the formation of silica gel is avoided;

separating the resulting solution from the solid insoluble residue; and

separately recovering the iron, lead, copper, calcium,

silicon, zinc and aluminum values in said slag from said solution andfrom said insoluble residue.

No references cited.

DAVID L. RECK, Primary Examiner.

N. F. MARKVA, Examiner.

1. A WET PROCESS FOR THE SEPARATION, ISOLATION AND RECOVERY OF THE ACID SOLUBLE METALLIC AND NON-METALLIC VALUES IN WASTE SLAG RESULTING FROM THE REVERBRATORY REFINING OF COPPER PYRITIC TYPE ORES WHICH COMPRISES: CRUSHING THE SLAG; ADDING A WARM SOLUTION OF AT LEAST ONE MINERAL ACID TO SAID CRUSHED SLAG, SAID SOLUTION HAVING A NORMALITY OF 4 AT THE TIME IT IS ADDED TO THE SLAG; MIXING THE SLAG AND ACID FOR NOT LESS THAN 8 MINUTES UNDER CONDITIONS SUCH THAT THE TWO ARE NOT PERMITTED TO REACH A TEMPERATURE OF 175*F., WHEREBY THE FORMATION OF SILICA GEL IS AVOIDED; SEPARATING THE RESULTING SOLUTION FROM THE SOLID INSOLUBLE RESIDUE; AND RECOVERING THE SOLUBLE IRON, LEAD, COPPER, CALCIUM SILICON, ZINC AND ALUMINUM VALUES ORIGINALLY PRESENT IN SAID SLAG FROM SAID SOLUTION. 